1. Technical Field
The present invention relates to a secondary battery, and more particularly, to a secondary battery having high durability against vibration and shock and has improved coupling of a cap assembly.
2. Discussion of Related Art
Typical batteries are classified into primary batteries and secondary batteries. The primary batteries are often disposable because they either cannot be charged or can only be charged very slowly. On the other hand, the secondary batteries exhibit reversible conversion between chemical energy and electrical energy, thus allowing for repetitive charging and discharging.
Secondary batteries may be classified into nickel batteries and lithium batteries depending on the active material of their electrode. In particular, an amount of energy that can be charged depends on materials of the electrodes and electrolyte. The lithium secondary batteries are capable of storing the most energy in the same volume and are widely used as power supplies for modern cell phones, notebook computers, camcorders, personal digital assistants (PDAs), etc.
The lithium secondary batteries use lithium oxide as a cathode active material and carbon oxide as an anode active material. The lithium secondary batteries may be classified into lithium ion batteries using liquid electrolyte and lithium polymer batteries using polymer electrolyte depending on electrolyte types. The lithium secondary batteries may be of several types, including a cylindrical type, a polygonal type, a pouch type, and the like.
Such a secondary battery generally comprises an electrode assembly having a cathode plate and an anode plate wound with a separator interposed therebetween, a case for accommodating the electrode assembly, and a cap assembly located on an opening of the case for sealing the case, with a gasket interposed between the cap assembly and the case.
Specifically, the cap assembly often comprises a top cap member or cap-up, a vent plate, an insulator, and a bottom cap member or cap-down.
The insulator is often vertically fastened with the vent plate. In this case, first fastening members of the insulator are coupled with insertion portions of the vent plate, causing the first fastening members to interfere with bent portions of the vent plate.
Since the interference with the bent portions increases with an increasing size of the first fastening member, the first fastening member is not allowed to increase above a predetermined size.
As a result, a coupling force between the first fastening members and the insertion portions to couple the insulator with the vent plate is limited and the insulator is more likely to rotate and be unloaded or otherwise dislodged due to possible vibration or shock.
The insulator and the cap-down are also coupled to each other by second fastening members of the insulator. In this case, the second fastening members vertically presses the cap-down to be fixed thereto. This may cause the cap-down to rotate due to possible vibration or shock.
The rotation of the cap-down may break a weld between the vent and the cap-down. Thus, a current path from the electrode assembly to the cap-up can be abnormally blocked impeding the normal operation of the battery.